Car keys were previously mechanical keys to unlock door locks and start engines. Due to the poor security performance, now mechanical keys are not used a lot. For present new cars, remote keyless entry and keyless start system are mainly used. A key of remote keyless entry is here called remote key. A key of keyless start system is here called smart key. The remote key and smart key are electronic keys. Remote key and smart key internally include key security chip, so that their anti-theft performance is good in many cases. However their anti-theft performance becomes even worse than the previous mechanical key if the electronic keys are lost. For example, the person who stole the remote key or smart key can easily find the car by pressing the door unlocking button from a far away distance and drive the car away. The remote key and smart key still include the mechanical key. When an old car is sold, the previous car owner can still open the car door with a spare mechanical key. If the mechanical key is lost, disabling the mechanical key takes time and money a lot. If the mechanical key is not disabled, whoever picked up the mechanical key can always take away the property inside the car. Remote key and smart key cannot be made for spare in most key stores, and the making in special stores takes high price and long time. Remote key and smart key are expensive. In comparison with mechanical key, remote key and smart key have poor waterproof, poor impact resistance, poor anti-electromagnetic interference ability, poor reliability because of built-in battery. Remote key and smart key are large and heavy, not convenient to carry.
Similar problems exist for the electronic keys for car, train, motorcycle, ship, aircraft and other vehicles, building, courtyard, safe, suitcase, bookcase, distribution box, equipment cabinet, drawer, container and other boxes and cabinets, padlock, chain lock and other independent locks.
Also, sometimes people forget and leave car mechanical key and remote key inside the car and lock the doors. The keys may also be lost. When the owner could not open the door and seek others for help, the owner needs spend time and money with psychological uneasiness. Especially, remote key and smart key are not interchangeable among car manufacturers, and the price is very expensive, so that many people are reluctant to spend money to buy spare car remote key and smart key.
In order to solve this problem, some cars mount an electronic keypad outside car door. However, most car electronic keypads are built-in type and expensive. The installation and removal generally are difficult for ordinary people and need professionals to do. Some cars mount electronic keypad with double-sided tape or adhesive outside car, however it is easily lost or stolen by other people. The present electronic keypad can unlock car door but cannot start engine. Therefore now total popularity rate of automobile electronic keypad is very low. In addition, some house doors mount keypad door lock, but keypad and lock are not separated, installation and removal are complicated, with high cost and poor water resistance.
There are previous patents as follows:    U.S. Pat. No. 7,362,211 B2, Huntzicker, F. W., 22 Apr. 2008. Door frame is used to prevent radio-electronic keypad from being stolen or lost, but the shape of the door frame is complicated, electronic keypad is still easy to lose, and easy to be squeezed to break by the door.    U.S. Pat. No. 7,595,718 B2, Chen, T. H., 2 Sep. 2009. There are protrusions outside installation structure of electronic keypads, which occupy door edge space. It is inconvenient to use, and the installation is not firm.    U.S. Pat. No. 8,410,897 B2, Popelard A., 2 Apr. 2013. Electronic keypad is mounted on car door handle. Installation and removal need professionals, and the cost is expensive.    U.S. Patent No. US 20060238385 A1, Steenwyk, T. E., et al, 26 Oct. 2006, Electronic keypad is mounted on car mirror. Repair and replacement need professionals, and the cost is expensive.
In addition, when people leave home or a car, an item that is most often carried is a key. Keys have the type of mechanical key, electronic card key, remote control key, etc. In order to do unified management of keys, many people bundle several keys to a keychain and carry together. However, except for unlocking and locking, keys are not useful. A keychain with several keys, if coupled with one or more large car remote control key, its volume becomes large and its weight increases a lot. People feel inconvenient to place a large heavy keychain in their cloth pocket. The case becomes worse when they also carry other items, or when they do exercise, jogging, gymnastics, etc.
On the other hand, mobile phones, smartphones, tablet PCs and other smart watches and portable electrical appliances are also the most commonly carried several items. These items are versatile items with many uses, many things cannot be done without them. Thus, people like to carry them.
If mobile phones, smartphones, smart watches, tablet PCs and other portable appliances increase key feature, especially a portable electrical appliance has the feature of several keys and is able to unlock several locks, it becomes much more convenient for people carry and manage articles. However since it does not work without electricity, the key function of mobile phone etc. is still not widely used.